November 2023:
After unlocking the phone, downgrading from fully up to date Android 13 to Android 11 ready to flash Sailfish “official recommended & tested way” showed to be and easy “one step” operation with Sony EMMA flashing tool on windows 10.
In Sony EMMA I used the first of 3 options: A.3.109 something. (Android version was not indicated as number 11 in EMMA but from the Sailfish support link below I got confirmation that this is indeed the right one:
“As of March 2023, the latest services were as below but note that the exact version ID’s can vary by model (regular/Plus/Ultra) and by sales area.”
Device Xperia 10 III
Android baseband version: 62.0. A.3.109 (Android 11)
For the rest “happy flashing” is an overstatement but the official guide worked well and I just found it not clear written in step 4.2 that you need to put the Sony SW_binaries_for_Xperia_Android_11_4.19_v9a_lena files and the Sailfish Sailfish_OS-Jolla-4.5.0.24-xqbt52-1.0.1.23 files together.in one folder to prepare for Sailfish flashing.
These file names where the ones official provided in the download links early Nov. 2023
No need to follow over the air updates of a certain version of Android 11 to reach a certain version number of 11 , relocking / unlocking boot loader etc… as some posters over time have mentioned.
Happy to report the tools (EMMA, Fastboot, drivers on Windows 10,…) and USB connections